Hisham Z. Massoud

Causes and Prevention of Temperature-Dependent Bubbles in Silicon Wafer Bonding

Unbonded areas or bubbles generated at the interface of bonded silicon wafers in the temperature range of 200-800°C have been investigated. Experiments described in this paper demonstrate that the desorption of hydrocarbon contamination at the silicon wafer surfaces appears to be a necessary condition for the formation of these bubbles. SIMS data also indicate the existence of hydrocarbons at the bonding interface. It is speculated that hydrocarbon gas such as CH4 is required for bubble nucleation and that either CH4 or H2 itself or a mixture of both gases is contained in these bubbles. Finally, methods to prevent the formation of these bubbles are presented.

Silicon Oxidation Studies: Silicon Orientation Effects on Thermal Oxidation

Abstract : The initial stage of the thermal oxidation of various crystallographic orientations of silicon reveals a complex rate behavior. This behavior is not understood within the conventional linear - parabolic model. A recently revised model which explicitly contains the areal density of Si atoms and mechanical stress effects is shown to provide both a qualitative and somewhat quantitative explanation of the complex substrate orientation effects. The purpose of this study is to analyze the crossover effect in terms of a recently proposed viscous flow model for Si oxidation. This model utilizes the notion of mechanical stress and viscous relaxation in Si02 which occur as a result of the oxidation process on a Si substrate in addition to the other assumptions in the L-P model such as a steady state between the interface reaction and the transport of oxidant through the oxide. It is reported herein that the new viscous flow model provides a reasonable qualitative explanation for the crossover effect and in some instances a quantitative correlation of the effect.

The effect of ion-implantation damage on dopant diffusion in silicon during shallow-junction formation

Low-thermal-budget annealing of ion-implanted BF2+, P, and As in Si was studied for shallow-junction formation. Implant doses were sufficient to amorphize the silicon surface region. Low-temperature furnace annealing and rapid-thermal annealing of ionimplanted boron, phosphorus and arsenic in silicon exhibit a transient enhanced diffusion regime resulting injunction depths considerably deeper than expected. The origin of this transient enhanced diffusion is the annealing of ion-implantation damage in the silicon substrate. We have found that point-defect generation during the annealing of either shallow end-of-range damage or small clusters of point defects dominates the transient enhanced diffusion process depending upon the annealing temperature and time. The net effect of damage annealing is to reduce the activation energy for dopant diffusion by an amount equal to the activation energy of the supersaturation of point defects in silicon. Models which can describe the transient enhancement characteristics in dopant diffusion during both furnace and rapid-thermal annealing of these implants are discussed.

Measurement and modeling of charge feedthrough in n-channel MOS analog switches

Charge feedthrough in analog MOS switches has been measured. The dependence of the feedthrough voltage on the input and tub voltages, device dimensions, and load capacitances was characterized. Most importantly, it was observed that the feedthrough voltage decreases linearly with the input voltage. The significance of this observation when considering harmonic distortion in sample-and-hold circuits is discussed. A first-order computer simulation based on the quasi-static small-signal MOSFET capacitances shows good agreement with experimental results.

Charge‐transfer dipole moments at the Si–SiO2 interface

A first‐order model has been developed to calculate the magnitude of the dipole moment at the Si–SiO2 interface resulting from partial charge transfer that takes place upon the formation of interface bonds. The charge transfer occurs because of the difference in electronegativity between the two species across the interface, namely silicon atoms and SiO2 molecules. This approach is similar to that introduced to describe the modification of band lineup at the Si–SiO2 interface by means of an intralayer of H or Cs. The charge‐transfer estimation uses the principle of electronegativity equalization, and results obtained for (100) and (111) silicon substrates indicate that the magnitude of the interface dipole is orientation dependent. Dipole moments at the Si–SiO2 and gate–SiO2 interfaces should be included in the definition of the flatband voltage VFB of metal‐oxide‐semiconductor structures. The metal‐semiconductor work function difference φms determined from capacitance‐voltage measurements on (100) and (1...

Analytical relationship for the oxidation of silicon in dry oxygen in the thin‐film regime

The oxidation of silicon in dry oxgen is characterized by an initial stage where the growth rate is larger than predicted by the Deal–Grove linear‐parabolic general oxidation relationship. This growth‐rate enhancement has been studied in the 800–1000 °C range by using in situ ellipsometry, and its dependence on the oxidation parameters has been analyzed. In this paper, the rate enhancement in the thin‐film regime is analyzed as a function of oxidation time and is found to fit two terms which decay exponentially with time. These results yield an analytical relationship between the oxide thickness and the oxidation time that describes SiO2 growth beyond the native oxide. The nature of the additional oxidation mechanisms and their decay with time is discussed.

An investigation of Si‐SiO2 interface charges in thermally oxidized (100), (110), (111), and (511) silicon

Trends in the electronic properties of the Si‐SiO2 interface with various processing have been frequently reported. The present study focuses on silicon substrate orientation dependent trends in fixed oxide charge, Qf, and interface trap charge, Dit, for four silicon orientations: (100), (110), (111), and (511), for oxidation temperatures in the 750–1100 °C range, with and without hydrogen‐containing post‐metal anneals, and for processing within and without a cleanroom. It is found that the presence of mobile ionic charge in non‐cleanroom processing and the lack of post‐metal annealing can either obscure or enhance some trends. Both Qf and Dit increase for decreasing oxidation temperature for all silicon orientations. The orientational ordering of the charges varies with oxidation temperature and is dominated by the silicon atom areal density at the lowest temperatures with (110) Si having the highest charge, but a change to the (111) orientation is observed at higher oxidation temperatures. This orientat...

The spectral grid method: a novel fast Schrodinger-equation solver for semiconductor nanodevice simulation

A spectral-domain method is described for solving Schrodingers equation based on the multidomain pseudospectral method and boundary patching. The computational domain is first divided into nonoverlapping subdomains. Using the Chebyshev polynomials to represent the unknown wave function in each subdomain, the spatial derivatives are calculated with a spectral accuracy at the Chebyshev collocation points. Boundary conditions at the subdomain interfaces are then enforced to ensure the global accuracy. Numerical results demonstrate that this spectral-domain method has an exponential accuracy and is flexible, and thus is an attractive method for large-scale problems. With only about four cells per wavelength, the results have an error less than 1% in our typical examples. For a typical quantum well, the method is about 51 and 295 times faster than the second-order finite-difference method for 1% and 0.1% accuracy, respectively. The spectral grid method has also been validated by results obtained by the finite-element method, semianalytical (Airy function) method, and the Numerovs method.

Rigid and flexible thin-film multielectrode arrays for transmural cardiac recording

Thin-film transmural cardiac multielectric arrays were fabricated using integrated-circuit processing techniques. Improvements over conventional handmade arrays, such as a smaller cross-sectional area, a larger number of recording sites per needle, more accurately controlled size and spacing of the recording sites, smaller bipolar spacings, and higher throughput yield, allow for a higher density of closely spaced bipolar electrodes capable of monitoring complex voltage and gradient fields present during ventricular fibrillation and defibrillation. Both rigid and flexible arrays were fabricated and used in the acquisition of transmural electrical signals. In vitro and in vivo testing of the thin-film transmural cardiac multielectrode arrays indicates that there are no adhesion or delamination problems, and no implantation difficulties, and that unipolar and bipolar recordings during normal sinus rhythm and injury potentials in unipolar recordings are similar to those obtained using the handmade electrodes.<<ETX>>

Manufacturability of rapid-thermal oxidation of silicon: oxide thickness, oxide thickness variation, and system dependency

The dependence of oxide thickness, and oxide thickness variation within a wafer and wafer-to-wafer on process variables was studied in rapid-thermal processing systems that differed in chamber configuration and construction, incoherent light source, and pyrometers used for temperature measurement. Mechanisms for oxide growth and oxide thickness variation in rapid-thermal oxidation are discussed. Thermally induced stress, lamp configuration, and convective cooling affected the oxide thickness variation within a wafer. Wafer-to-wafer oxide thickness variation depended on the material of chamber construction, quartz or metal, and was related to residual heating for longer oxidations. For the same processing conditions, the oxide thickness was different for different systems, due to temperature error and a photonic component to rapid-thermal oxidation. Analysis of empirical oxide thickness models revealed a silicon orientation effect and a mechanism related to oxidant transport that was common to rapid-thermal oxidation in different systems. >